Investigating herbicide targets in the very long-chain fatty acid biosynthetic pathway
Résumé
Very-long-chain fatty acids (VLCFA), with 20 or more carbons, are essential molecules with significant physiological and structural functions in plants because they are components of key lipids such as membrane phospholipids and sphingolipids, seed triacylglycerols, cuticular waxes and root suberin. The elongation of VLCFA is carried out by the Fatty Acid Elongase complex which performs a four-step reaction cycle that adds two carbons to the growing fatty acyl chain. KCS enzymes, which are responsible for the first condensation reaction, are known for their high genetic diversity in plants, and functional characterization of several Arabidopsis KCS genes has revealed different chain-length specificities. Herbicides that inhibit VLCFA synthesis (HRAC group 15) play a crucial role in weed management strategies. The mode of action of these compounds was initially identified based on the characteristic phenotype observed in treated plants, suggesting that they target the KCS subunit of the FAE complexes. Most commercially available herbicides exhibit stronger activity against grass plants (monocotyledonous) than broadleaf plants (dicotyledonous), though the reasons for this selectivity are not well understood. The objective of this project was to further explore the inhibition of VLCFA synthesis by HRAC 15 group herbicides. To do so, a phylogenetic analysis and a comparative functional analysis of KCS from various plant species were performed using a yeast heterologous system reconstituting complete plant FAE complexes. In addition, in vivo and in vitro studies using yeast expressing active KCSs treated with several herbicides, were conducted to investigate their mode of action and selectivity.
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